posted by Rod McCoremick, Blog author, Fordia Powered by Epiroc
July 16, 2018
Surface set core bits still have a role to play, and with the introduction of synthetic diamonds, surface set bits have become a lower cost alternative that are suitable for a variety of soft ground conditions. This kind of core bit is manufactured using a choice of diamond grades ranging from coarse to fine, and a variety of profiles, to make the core bits suitable for a range of ground conditions.
Choosing the right core bit is one of the most important decisions you will have to make and the same applies to surface set core bits. These are some of the factors you will need to consider when choosing a surface set core bit.
Surface set diamond core bits are the ideal choice for ground that is softer as they provide a lower cost for longer bit life. It isn’t necessary to use a higher cost diamond impregnated tool for softer grounds when a less expensive surface set bit will do the job. For very soft to soft ground, a surface set bit made with synthetic diamonds with is an ideal choice and represents the lowest cost.
When choosing surface set diamond core bits, you must look at the diamond grade. The grade represents the number of stones per carat (SPC) and not the quality of the stones. The harder the rock is, the smaller the diamond. So a SPC of 10/12 means there are between 10 and 12 diamonds per carat, which is ideal for very soft ground, or up to 2 on Mohs scale. An SPC of 60/80 means that there are between 60 and 80 diamonds per carat (much smaller diamonds) making it more suitable for medium hard ground, or 4 to 5 on Mohs scale.
Beyond the hardness of the ground, the condition of the ground will play a role in choosing the type of surface set bit you need. Surface set bits come in a variety of profiles that are suitable for different ground conditions. The semi-round profile is the standard and is suitable for most ground conditions. A round profile is better suited to abrasive ground with rocks.
If drilling in fractured ground, you may opt for an angled pilot profile, or a face discharge profile for very fragile ground.
When a fast rate of penetration (ROP) is required, a surface set bit with a step profile is a good choice but you must be cautious of the ground is fractured as it can be fragile. The pilot profile is good for soft to medium ground and provides good stability as well as good ROP and recovery.
As mentioned above, choosing a surface set bit with synthetic diamonds is the most economical choice. But surface set core bits made with natural diamonds are still less expensive than diamond impregnated bits. When ground conditions allow, opting for a surface set bit will cost less.
To sum up, surface set diamond core bits are a low cost alternative when a higher cost, diamond impregnated core bit is not necessary. This is usually the case when you are drilling in softer ground. And as explained above, surface set bits come in different profiles. If you want more information or guidance in choosing surface set diamond core bits, do not hesitate to contact our tech support team. Custom surface set bits with other diamond grades can also be ordered for special requirements.